Process and composition for phosphatizing metals



United States Patent assignors to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation oi New York No Drawing. Filed Mar. 21, 1960, Ser. No. 16,126 20 Claims. (Cl. 1.48-6.15)

This invention relates to a process and composition for phosphatizing metals. More particularly, this invention relates to an improved, substantially water-free phosphatizing liquid, and to the process for applying phosphate coatings to metal surfaces with such a phosphatizing liquid.

Phosphate coatings are applied to metal surfaces to prevent oxidation of the metal and to condition the metal surfaces for applying paint finishes. Metal surfaces should be free from rust, oil and other extraneous substances in order to obtain a uniform, hard phosphate coating. Therefore, the metal is cleaned in inorganic solutions such as hot alkaline solutions, in organic solutions such as chlorinated hydrocarbons, or otherwise cleaned prior to phosphatizing. In one method of cleaning, metal articles which may be coated with a film of rust-preventative oil, called slushing oil, are first subjected to a degreasing operation in which the oil and extraneous materials are removed by contacting the metal with a chlorinated hydrocarbon, such as trichloroethylene, perchloroethylene, and trichloroethylene in liquid and/or vapor form.

Several methods for applying phosphate coatings to degreased metal surfaces have been previously employed. In one method, which is referred to as the aqueous method, the metal is cleaned in a hot alkaline solution, rinsed, immersed in a hot aqueous phosphatizing solution, then rinsed, immersed in chromic acid, and dried. Such a process has the disadvantage of requiring a large number of expensive operating steps. In addition, sludge rapidly builds up in the aqueous phosphatizing solution, thereby inhibiting the efiectiveness of the phosphatizing bath. In another process, which is referred to as the dry process, the degreased metal is immersed in a solution of phosphoric acid and an organic solvent, such as acetone, carbon tetrachloride, lower alcohols, and the like. Phosphatizing solutions such as these have relatively low boiling points, and as a result, large proportions of thesolvent are lost by vaporization. In addition, these phosphatizing baths have relatively low flash points. in another dry process the phosphatizing path consists of trichloroethylene, phosphoric acid and an alkyl acid phosphate. In phosphatizing baths of this type, the alkyl acid phosphate solvent may react with the metal, thereby introducing potentially harmful substances on the metal surface. Furthermore, the free phosphoric acid content of the bath cannot be readily determined by simple titration procedures because of the interference of the ialkyl acid phosphate. In addition, rinsing of the coated panel is necessary prior to painting.

It is an object of this invention to provide an improved composition for phosphatizing metals.

It is another object of this invention to provide an improved process for phosphatizing metals.

Still another object of this invention is to provide an improved phosphatizing composition which is relatively nonflammable and which is substantially water-free.

A further object of the invention is to provide an improved phosphatizing composition containing a novel inhibitor which enhances the. formation of hard, uniform, impervious microcrystalline phosphate coatings on metal surfaces. 7

3,100,728 Patented Aug. 13, 1963 "ice It is a further object of the invention to provide a novel phosphatizing composition which contains organic compounds which are susbtantially non-reactive with metals.

These and other objects of the invention will be apparent from the following description.

It has now been discovered that thin, uniform, hard, impervious microcrystalline phosphate coatings are readily formed on degreased metal surfaces when the metal surfaces are contacted with a solution of chlorinated hydrocarbon, phosphoric acid, alcohol and glacial acetic acid. vIn addition, metals coated with such a solution can be readily painted to yield a finish having improved resistance to corrosion by salt spray and water. When glacial acetic acid is omitted from the phosphatizing bath, and phosphatizing is effected under the conditions described below, the resulting phosphate coatings are porous, macrocrystalline, thick and otherwise unsatisfactory.

Any metal of the class capable of reacting with phosphoric acid to form the corresponding metal phosphate, such as iron, aluminum, zinc, magnesium, cadmium, al-

loys containing these metals, and the like may be treated in accordance with the instant novel process.

Prior to phosphatizing, the metal is cleaned by any suitable means such as by employing chlorinated hydrocarbon to remove oil and extraneous material. The chlon'nated hydrocarbon is preferably maintained at or near the boiling point, and the metal to be cleaned is contacted with the liquid phase and/ or the vapor phase. The metal article, which has been cleaned in the chlorinated hydrocarbon, or otherwise cleaned, is then contacted with a phosphatizing solution containing the following ingredients in the following proportions:

Percentage Preferred Component by weight percentage by Weight Chlorinated hydrocarbon... 70 -98 85 97 Phosphoric acid 0.1- 6 0.6- 2 Alcohol 1.5-25 3 15 Glacial acetic acid 0.1- 0 5 0.2- 0.4

' chloroethylene, trichloroethanes, tetrachloroethanes, methylene chloride, ethylene chloride, ethylidene chloride and the like.

It is preferred to employ a chlorinated hydrocarbon containing a stabilizing composition, but unstabilized chlorinated hydrocarbons can be employed if desired. Typical examples of stabilizers which may be suitable include: olefins, as described in U.S. Patent Nos. 1,904,450 and 2,435,312; acetylenic compounds, as disclosed in U.S. Patent Nos. 2,775,624 and 2,803,676; hydrocarbons, as disclosed in U.S. Patent Nos. 1,816,895 and 1,858,022; phenols, as disclosed in U.S. Patent Nos. 2,008,680 and 2,155,723; alcohols, as disclosed in U.S. Patent Nos. 2,775,624 and 2,887,516; esters, as disclosed in U.S. Patent No. 2,371,646; ethers and epoxides, as disclosed in U.S. Patent No. 2,371,645; heterocycles containing N and O or S in ring, as disclosed in U.S. Patent No. 2,517,- 893; aldehydes, as disclosed in U.S. Patent No. 1,151,255; rnercaptans, as disclosed in U.S. Patent No. 1,917,073; alkyl cyan'amides, as disclosed in U.S. Patent No. 2,043,- 257; alkyl thioureas, as disclosed in U.S. Patent No.

2,043,258; alkyl amines, as disclosed in U.S. Patent No. 2,096,735; aryl amines, as disclosed in U.S. Patent No.

2,094,367; alkyl isocyanates, as disclosed in U.S. Patent No. 2,108,390; \guanidines, as disclosed in U.S. Patent No. 2,125,381; diols, as disclosed in U.S. Patent No.

. 3 V 2,355,319; oXimes, as disclosed in U.S. Patent No. 2,371,- 647; keton'es, as disclosed in U.S. Patent No. 2,376,075; nitriles, as disclosed in U.S. Patent No. 2,422,556; amides, as disclosed in U.S. Patent No. 2,423,343; nitrates, as disclosed in U.S. Patent No. 2,436,772; thiophenes, as

' disclosed in U.S. Patent No. 2,440,100; pyrroles, as disclosed in U.S. Patent No. 2,492,048; nitroalkanes, as disclosed in U.S. Patent No. 2,567,621; sulfones, as disclosed in U.S. Patent No. 2,742,509; azines, as disclosed in U.S. Patent No. 2,878,297; aryl stibines, as disclosed in U.S. Patent No. 2,917,554; sulfoxides, as disclosed in U.S. Patent No. 2,919,295; and mixtures thereof. This list of stabilizers is intended to be illustrative, and is not an exhaustive list.

Some of the mixtures of the stabilizers may have a synergistic effect under certain phosphatizing conditions as evidenced by the elimination or inhibition of reaction products, oxidation products, hydrolysis products, polymer'mation products, decomposition products and the like.

Since the chlorinated hydrocarbons are relatively nonflammable and have a relatively high flash point compared to alcohols, it is preferred to use the highest proportion of chlorinated hydrocarbon in the bath consistent with obtaining a smooth, uniform phosphate coating on the metal.

It is preferred to employ'highly concentrated orthophosphoric acid such as the eighty-five percent phosphoric acid of commerce, but more dilute or more concentrated acid solutions can be employed if desired. Regardless of the acid concentration initially employed, substantially all of the water is ultimately distilled from the phosphatizing bath as the phosphatizing treatment progresses. The phosphatizing proportion of phosphoric acid referred to in the description and claims may be between about 0.1 and about 6%, and preferably between about 0.6 and about 2% by weight of the phosphatizing solution.

Since concentrated phosphoric acid is insoluble in chlorinated hydrocarbons, it is necessary to employ an alcohol in the above defined proportions to dissolve the phosphoric acid in the chlorinated hydrocarbon liquid. Any aliphatic or alicyclic rnonohydroxy alcohol capable of dissolving phosphoric acid in the chlorinated hydrocarbon solution may be employed; Typical examples of suitable alcohols include the alcohols which contain between one and about eighteen carbon atoms such as methanol, ethanol, n-propanol, isopropan'ol, n-butanol, isobutanol, tertiary b-utanol, tertiary amyl alcohol, octanol, decyl alcohol, lauryl alcohol, stearyl alcohol, cyclohexyl alcohol and mixtures thereof. Since the solubility of phosphoric acid is less in the higher alcohols than in the lower alcohols, it is preferred to employ an alcohol having less than about ten carbon atoms, and more preferably between on'e and about six carbon atoms.

It has been noted that normal butyl alcohol has several advantages when compared to other alcohols. Firstly, when trichloroethylene is employed as the chlorinated hydrocarbon, a but-anol-trichloroethylene azeotrope forms which boils at a temperature (eighty-six and sixty-five hundredths degrees centigrade) slightly below the boiling temperature of trichloroethylene (about eighty-seven degrees centigrade); The azeotropes formed with many other alcohols boil at somewhat lower temperatures. Secondly, normal butanol dissolves a higher proportion of phosphoric acid than other alcohols, thus requiring less alcohol solvent. Thirdly, the normal butyl alcohol-trichloroethylene azeotrope-contains about 2.5 percent by Weight of normal butyl alcohol, thus effecting a concentration of the alcohol in the phosphatizin'g solution, when the initial concentration of alcohol in the phosphatizing solution is greater than about 2.5 percent by weight. Thus, depletion of the alcohol in the pot, which may cause the formation of two liquid phases, due to the insolubility of phosphoric acid in the chlorinated hydrocarbon, is avoidedand the need for close control of the tween about fifty-five and about square foot.

tween about ten and about fifty 'phatizing of metal articles.

concentration of normal butyl alcohol in the pot is greatly reduced.

It is important to add an inhibiting proportion of a polar compound such as glacial acetic acid to the phosphatizing solution in the above described proportions in order to obtain the desired properties in the resulting phosphate coating. The inhibiting proportion of glacia-l acetic acid referred to in the description and claims may be between about 0.1 and about 0.5% and is preferably between about 0.2 and about 0.4% by weight of the phosphatizing solution.

It has been found that when glacial acetic acid is employed as a component of the phosphatizing solution in the proportions set forth above, the resulting phosphate coating is smooth, uniform, hard and microcrystalline. The phosphate coating in such a case is generally of the order of between about twenty-five and about two hundred and fifty milligrams per square foot. However, under practical operating time and temperature conditions, if the phosphatizing solution contains greater than about 0.6 percent phosphoric acid by weight, and either less than about 0.1 percent or greater than about 0.5 percent by weight of glacial acetic acid, the resulting phosphate coatings are heavy, porous, uneven, and macrocrystalline. In the latter case the phosphate coating generally Weighs in excess of about three hundred milligrams per square foot and is occasionally over one gram per The porous nature of the phosphate coating obtained when glacial acetic acid is employed in proportions outside the above specified ranges probably accounts for the poor paint-bonding properties which result.

In the process for applying the phosphate coating, the degreased metal is contacted with the novel phosphatizing solution described above for a period of time up to about thirty minutes and preferably between about 0.5 and about fifteen minutes. The bath is maintained at a temperature between about twenty degrees centigrade and the boiling point of the solution, and preferably beseventy degrees centig-rade, the higher temperatures usually being employed when the shorter contact times are employed.

The words contacted" and contacting, as used throughout the description and claims in connection with treating the metal with the phosphatizing solution are intended to include wetting the metal article with the solution by immersion, dipping, spraying and the like.

'If desired, the phosphatized metal, after removal (from the bath, may be returned to the chlorinated hydrocarbon ldegreasing solution for a final rinse to remove phosphatizing solution, but this step is often not necessary since the phosphatized metal is generally substantially dry when removed from the phosphatizin g bath. The phosphatized metal article, with or without rinsing, as the case may be, can be stored or used as is. If desired, the phosphatized metal may be subjected to iurther treatment such as painting, lubricating and the like. The phosphate-coated metals resist corrosion and retain paint finishes as well as or better'than metals phosphatized by conventional aqueous or dry processes.

It has been found that the effectiveness of the novel phosphatizing solution is enhanced on start-up by admixing the solution with a small proportion of powdered iron or other metals of the class being treated (i.e., between about 0.01 and about 0.1 percent by Weight of solution), heating the resulting slurry to between about fiftyfive degrees Centigrade and the boiling point for beminutes, and then separating suspended solids from the slurry by filtering or the like, prior to employing the solution in the phos- When a novel phosphatizing solution has not been so treated with iron powder, occasionally the first one or two articles coated with the untreated phosphatizing solution have phosphate coatings that are not as satisfactory as the coatings of the metal articles subsequently produced from the phosphate solu- The [following examples are presented to define the invention more fully without any intention of being limited thereby. All parts and percentages are by weight unless otherwise specified.

Examples 1-6 Trichloroethylene (eleven hundred and fifty grams), eighty-five percent phosphoric acid (fourteen grams), and normal butyl alcohol (sixty-five grams) were admixed with powdered iron (one hundred miligrams) for thirty minutes at sixty degrees centigrade, then filtered through [glass wool, and the resulting clarified phosphatizing solution was recovered.

Bare steel panels, twenty-four gauge, three inches by five inches, were employed in these tests.

Six groups of three panels each (designated as groups A, B, C, I), E and F, respectively), were degrcased in trichloroet-hylene vapors. Group A panels were immersed in the aforesaid clarified phosphatizin-g solution at a temperature of sixty-five degrees centigrade for about five minutes each to effect a phosphate coating thereon.

After removal of the panels, 2.1 grams of glacial acetic acid were admixed with the phosphatizing bath and group B panels were then phosphate coated therein in the same manner as group A. The panels of groups C, D, and B were treated in the same manner, with the exception that the concentration of glacial acetic acid was increased for each group in the proportions set forth in the following table:

Total weight Percent by Panel group of acetic acid weightof added, grams acetic acid in solution Each of the fifteen panels in groups A through E, after coating in the phosphatizing bath were rinsed in trichloroethylene vapors. One panel from each of the five groups was treated to determine the weight of phosphate coating thereon by stripping the phosphate coating in an alkaline solution of sodium cyanide as described in Industrial Finishings, volume 9, page 878, 1957. The weight Three degreased, non-phosphatized panels (designated as group F), and the remaining ten phosphate coated panels from groups A through E, were then painted by rolling with a white baking enamel, then baked for thirty minutes at one hundred and sixty degrees centigrade, and aged for about twenty-four hours. The two panels (group A) that had been phosphate coated in the solution free from glacial acetic acid were discarded because the paint coating was blistered extensively. The remaining eleven painted panels were then subjected to a salt fog spray test, employing the salt fog spray technique, described in ASTM Designation No. B-117-54T. In this test each panel was scored vertically with a sharp steel knife and subjected to an atomized fog of a five percent aqueous sodium chloride solution at a temperature of about ninety-five degrees Fahrenheit for about seventy-two hours. The panels were then rinsed in water and wiped \dry. A one-inch wide stainless steel spatula was then scraped along the score mark. The width of the area of paint removed by scraping was as follows:

Width of paint area scraped Panel from panel, mm. group Conditions for treating panel Panel #1 Panel #2 Panel #3 B 0.19% glacial acetic acid in 0 1.

bath. 0 0.37% glacial acetic acid in 1 1 bath. D 0.74% glacial acetic acid in bath. E 1.47% glacial acetic acid in bath. F No phosphate coating 11.0 6.9 16.7

1 Paint soft, width could not be evaluated.

From the above table it can be seen that panels phos phatized in accordance with the instant novel process (groups B and C), attained superior paint bonding properties under highly corrosive conditions.

The eleven painted panels of groups B through F, after completion of the salt fog spray test, was subjected to a tape test wherein a V was scribed through the paint coating to the bare metal. The legs of the V were about one inch long and the opening of the V was about half an inch wide. Cellophane adhesive tape was rubbed and pressed into intimate contact with the coating and covered the V such that a threc-inch tail of tape was left loose above the apex of the V. The tape was then pulled back suddenly in a manner such that it was removed at an angle of about one hundred and eighty degrees to itself. The paint removed around the V determined the adhesion of the paint in accordance with the following rating system:

( (9) Trace of peeling (10) No peeling Peeling beyond lines and tape Peeling beyond lines, but under tape Peeling within lines, entire area Peeling within lines, greater than half the area Peeling within lines, greater than one-quarter the area Peeling within lines, less than one-quarter the area lagged peeling along cuts to one-eighth inch Smooth peeling along cuts to one-eighth inch 1 The paint on these panels was soft in some areas and hard in others Thus, the tape test rating varied from about 5 to about 9 on these panels, depending upon which area of the panel was tested.

This table further demonstrates the superior paint bonding properties of metals phosphate-coated in accordance with the instant novel process.

It will be recognized by those skilled in the art that various modifications within the invention are possible, some of which have been referred to above. Therefore, we do not wish to be limited except as defined by the appended claims.

We claim:

'1. A substantially water-free composition of matter suitable tor phosphatizing metals consisting essentially of a chlorinated hydrocarbon containing a minor proportion of a monohy'droxy alcohol selected from the group consisting of aliphatic monohydroxy alcohols, alicyclic monohydroxy alcohols, and mixtures thereof, a phosphatizing proportion of orthophosphoric acid, and an inhibiting proportion of glacial acetic acid equivalent to between about 0.1 and about 0.5 percent by weight of said composition.

2. The composition of claim 1 wherein said chlorinated hydrocarbon is trichloroethylene.

3. The composition of claim 1 wherein said chlorinated hydrocarbon is perchloroethylene.

4. The novel composition of claim 1 wherein said alcohol contains between about one and about six carbon atoms.

5. A substantially water free composition of matter suitable for phosphatizing metals consisting essentially of between about seventy and about ninety-eight percent by weight of a chlorinated hydrocarbon, between about 1.5 and about twenty-five percent by weight of a monohydroxy alcohol selected lfrom the group consisting of aliphatic monohydroxy alcohols, alicyclic monohydroxy alc'hols, and mixtures thereof, between about 0.1 and about six percent by weight of orthophosp'horic acid,- and between 0.1 and about 0.5 percent by weight of glacial acetic acid.

6. The composition of claim 5 wherein said chlorinated hydrocarbon is trichloroethylene.

7. The composition of claim 5 wherein said chlorinated hydrocarbon is perchloroethylene.

8. The composition of claim 5 wherein said alcohol contains between about one and about six carbon atoms.

9. A substantially water-free composition of matter suitable for phosphatizing metals consisting essentially of between about eighty-five and about ninety-seven percent by weight of a chlorinated hydrocarbon, between about three and about fifteen percent by weight of a monohy- .droxy alcohol selected from the group consisting of aliphatic mono-hydroxy alcohols, alicyclic monohydroxy alchols, and mixtures thereof, between about 0.6 and about two percent by weight of orthophosphoric acid, and between about 0.2 and about 0.4 percent by weight of glacial acetic acid.

10. The process of phosphate-coating an article made of a metal of the class capable of reacting with phosphoric acid to form a metal phosphate which consists essentially of contacting said article with a composition comprised of a chlorinated hydrocarbon containing a minor proportion of a monohydroxy alcohol selected from the group consisting of aliphatic monohydroxy alcohols, alicyclic monohydroxy alcohols, and mixtures thereof, a phosphatizing proportion of orthophosphoric acid, and an inhibiting proportion of glacial acetic acid equivalent to between about 0.1 and about 0.5 percent by weight of said composition.-

11. The process of c1aim10 wherein said chlorinated hydrocarbon is trichloroethylene.

*12. The process of claim wherein said chlorinated hydrocarbon is perchloroethylene.

13. The process of claim 10 wherein said alcohol is normal butyl alcohol.

14. The process of phosphate coating an article of a metal of the class capable of reacting with phosphoric acid to form a metal phosphate which consists essentially of contacting said article rfor up to about thirty minutes at a temperature between about twenty degrees centigrade and about the boiling point with a composition comprised of between about seventy and about ninetyeight percent by weight of a chlorinated hydrocarbon, between about 1.5 and about twenty-five percent by weight of a monohydroxy alcohol selected from the group consisting of aliphatic monohy-droxy alcohols, alicyclic monohydroxy alcohols, and mixtures thereof, between about 0.1 and about six percent by weight of iorthophosphoric acid, and between about 0.1 and about 0.5 percent by weight of glacial acetic acid.

15. The process of claim 14 wherein said chlorinated hydrocarbon is trichloroethylene.

16. The process of claim 14 wherein said chlorinated hydrocarbon is perchloroethylene.

17. The process of claim 14 wherein said alcohol contains between about one and about six carbon atoms.

18. The process of phosphate-coating an article of a metal of the class capable of reacting with phosphoric acid to form a metal phosphate which consists essentially of contacting said article :for between about 0.5 and about fifteen minutes at a temperature between about fifty-five and about seventy degrees centigrade with a composition comprised of between about eight-five and about ninetyseven percent by weight of a chlorinated hydrocarbon, between about three and about fifteen percent by weight of a monohydroxy alcohol selected from the group consisting of aliphatic monohydroxy alcohols, alicyclic monohydroxy alcohols, and mixtures thereof, between about 0.6 and about two percent by weight of orthophosphoric acid, and between about 0.2 and about 0.4 percent by weight of glacial acetic acid.

19. The process of solubilizing phosphoric acid in a chlorinated hydrocarbon which comprises admixing said acid with said hydrocarbon in the presence of from about 1.5 percent to about twenty-five percent by weight of a monohydroxy alcohol selected from the group consisting of aliphatic monohydroxy alcohols, alicyclic monohydroxy alcohols, and mixtures thereof, and between about 0.1 and about 0.5 percent by weight of glacial acetic acid.

20. The process of claim 19 wherein said chlorinated hydrocarbon is trichloroethylene.

References Cited in. the file of this patent UNITED STATES PATENTS 2,515,934 Verher et al. July 18, 1950 2,702,768 Hyarns et al. Feb. 22, 1955 2,789,070 Copelin Apr. 16, 1957 2,992,146 Low July 11, 1961 FOREIGN PATENTS 22,743 Great Britain O ct.' 10, 1910 of 1909 i 

1. A SUBSTANTIALLY WATER-FREE COMPOSITION OF MATTER SUITABLE FOR PHOSPHATIZING METAL CONSISTING ESSENTIALLY OF A CHLORINATED HYDROCARBON CONTAINING A MINOR PROPORTION OF A MONOHYDROXY ALCOHOL SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC MONOHYDROXY ALCOHOLS, ALICYCLIC MONOHYDROXY ALCOHOLS, AND MIXTURES THEREOF, A PHOSPHATIZING PROPORTION OF ORTHOPHOSPHORIC ACID, AND AN INHIBITING PROPORTION OF GLACIAL ACETIC ACID EQUIVALENT TO BETWEEN ABOUT 0.1 AND ABOUT 0.5 PERCENT BY WEIGHT OF SAID COMPOSITION. 